Hello, I have a weird behavior and found solution that may interest others
Context: - All servers are VM under VMware ESXi 5.5, even ZLB - All VM having VMXnet 3 virtual nic issue: When doing L4xnat, With one frontend server, badnwidth is terribly slow. It's FTP service that is used. I am the only one, copying 1 big file. As soon as I start, ZLB keep sending ICMP packets to the FTP server: 14:45:54.829302 IP ZLBIPADDR > FTPSERVER: ICMP prd-sta-slb01.intern.mobistep.net unreachable - need to frag (mtu 1500), length 556 I checked everywhere, MTU is 1500. Now If I put the second FTP server, which is even accross a vpn, then no ICMP, and great bandwidth (11MB/s instead of 40KB/s) These 2 FTP servers are also Web server, load balancer through the same ZLB as web farm, not a single ICMP message. After digging with Wireshark, yes the slow one is sending packet bigger than MTU. This server is on same vswitch as ZLB internal card. It appeard that VMware nic do offloading and so then bigger packet than MTU. Everything is ok as soon as I disable TCP offloading on FTP server: *ethtool -K ens160 tx off sg off tso off* Maybe someone have a better config on ZLB to avoid that? Regards, Mathieu CHATEAU http://www.lotp.fr
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